mixin automatic getter/ setter & initialization

Sencha Touch version tested:

2.0.0 release

Browser versions tested against:

chrome, safari on ipad

DOCTYPE tested against:

<!DOCTYPE html>

Description:

This was my first try to use mixins as described in docs-> "Mixins are just classes".
So I defined a class with some config properties, a constructor, initialize method etc. (have a look onto the tester I provided)
I had a look onto the sources how e.g. Ext.dataview.DataView uses the selectable mixin.
It calls the constructor of the mixin in its constructor to initialize the mixin.

I reproduced the same, and afterwards I set some information to the mixin class by using the automatic getter and setter created by the config methods. These getter/ setter are initially available but vanish after
setting a value.

(->GenerateSetter method in line 5217, class Ext.class )

Code:

delete this[getName];

Afterwards getter are not available anymore, thus fail on call.

Two questions:
1. As these mixins should just be classes like all the others, I guess this is supposed to work?
2. Most of the Sencha Touch classes provide out of the box functionality for initialization, why does the mixins work different?
->Did I do the right thing?

Steps to reproduce the problem:
Just run the code in test case.

The result that was expected:
working setter and getters.

The result that occurs instead:
exception that method is not available due to removal as described above.